Electromagnetic telemetry system

ABSTRACT

An electromagnetic telemetry (EMT) system is provided. A downhole transceiver sub is coupled with a downhole tool. The downhole transceiver sub and the downhole tool positioned in a wellbore having a casing extending along a length of the wellbore. The downhole transceiver sub transmits data from the downhole tool by passing a current through the casing to radiate electromagnetic fields. An uphole transceiver sub is disposed uphole from the downhole transceiver sub. The uphole transceiver sub is operable to measure the electromagnetic fields. The measured electromagnetic fields are decoded to obtain the data from the downhole tool.

FIELD

The present disclosure relates generally to electromagnetic telemetry (EMT) systems used in a wellbore system. In particular, the present disclosure relates to EMT systems utilizing a casing in a wellbore to wirelessly transmit signals.

BACKGROUND

Wellbores are drilled into the earth for a variety of purposes including accessing hydrocarbon bearing formations. A variety of downhole tools may be used within a wellbore in connection with accessing and extracting such hydrocarbons. The downhole tools may require instructions and/or may need to pass along data obtained by the downhole tools. Telemetry is often performed via an electrical cable or fiber optic cable inside a conveyance, for example coiled tubing. In the absence of such a wired telemetry system, downhole tools may need to be set via a timing mechanism, or triggered by a mechanical event from the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by way of example only, with reference to the attached figures, wherein:

FIG. 1A is a diagram illustrating an exemplary environment for an EMT system according to the present disclosure;

FIG. 1B is a diagram illustrating a downhole transceiver sub;

FIG. 2 is a diagram illustrating a second example of an EMT system;

FIG. 3 is a diagram illustrating a third example of an EMT system;

FIG. 4 is a diagram of a processing system which may be employed as shown in FIGS. 1A-3; and

FIG. 5 is a flow chart of a method for utilizing an EMT system.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.

Disclosed herein is an electromagnetic telemetry (EMT) system for use in a wellbore system, which can include any or all of the following features or aspects in any given example. The wellbore includes a casing which is electrically conductive, such as steel. The EMT system includes a downhole transceiver sub and an uphole transceiver sub. The downhole transceiver sub includes a first electrode in contact with the casing and a second electrode in contact with the casing at a location uphole of the first electrode. The uphole transceiver sub includes a first electrode and a second electrode. In at least one example, the first electrode is in contact with the casing while the second electrode is in contact with the ground a predetermined distance away from the first electrode.

The downhole transceiver sub can be, for example, communicatively coupled with one or more downhole tools. The downhole tools can be, for example, downhole sensors, chokes, and valves. The chokes and valves may include actuatable flow regulation devices, such as variable chokes and valves, and may be used to regulate the flow of the fluids into and/or out of the conveyance. Additionally, data captured by the downhole sensors may need to be transmitted uphole. As such, the downhole tools may need to receive signals from a surface location for instructions on operation based on these signals. The downhole tools may also need to transmit signals to a surface location for analysis or to determine the next operation.

The downhole transceiver sub and the uphole transceiver sub can each receive and transmit wireless signals. For example, for the downhole transceiver sub to transmit signals to the uphole transceiver, a current is generated and passed between the first electrode and the second electrode of the downhole transceiver sub through the casing. The current can be an alternating current. In at least one example, the current can be a time-varying current. The electrically conductive casing forms a short circuit between the first and second electrodes of the downhole transceiver sub, and the current forms a finite-length electric dipole antenna which radiates electromagnetic fields into the formation. The electromagnetic fields can be measured by the uphole transceiver sub by measuring the voltage between the first electrode and the second electrode of the uphole transceiver sub. The measured electromagnetic fields can then be decoded to obtain the data from the downhole tools.

A similar process can be utilized to transmit signals from the uphole transceiver sub to the downhole transceiver sub. Current is passed between the first and second electrodes of the uphole transceiver sub which forms an electric dipole antenna. The voltage between the first and second electrodes of the downhole transceiver sub can be measured to measure the electromagnetic fields from the electric dipole antenna. The measured electromagnetic fields can then be decoded to obtain the data from the surface, or from the tool connected to the uphole transceiver sub. Accordingly, the EMT system disclosed herein provides for a wireless telemetry system within a cased wellbore.

The EMT system can be employed in an exemplary wellbore system 10 shown, for example, in FIG. 1A. A system 10 for a downhole tool 50 in a wellbore includes a drilling rig 12 extending over and around a wellbore 14. The wellbore 14 is within an earth formation 22 and has a casing 20 lining the wellbore 14, the casing 20 is held into place by cement 16. The casing 20 is at least partially made of an electrically conductive material, for example steel. The downhole tool 50 can be moved down the wellbore 14 via a conveyance 18 to a desired location. A conveyance 18 can be, for example, tubing-conveyed, wireline, slickline, work string, coiled tubing, or any other suitable means for conveying downhole tools into a wellbore. The downhole tools 50 can be, for example, downhole sensors, chokes, and valves. The chokes and valves may include actuatable flow regulation devices, such as variable chokes and valves, and may be used to regulate the flow of the fluids into and/or out of the conveyance 18.

It should be noted that while FIG. 1A generally depicts a land-based operation, those skilled in the art would readily recognize that the principles described herein are equally applicable to operations that employ floating or sea-based platforms and rigs, without departing from the scope of the disclosure. Also, even though FIG. 1A depicts a vertical wellbore, the present disclosure is equally well-suited for use in wellbores having other orientations, including horizontal wellbores, slanted wellbores, multilateral wellbores or the like.

As illustrated in FIG. 1A, the EMT system 60 includes a downhole transceiver 100 and an uphole transceiver 190. The downhole transceiver 100 is disposed within the wellbore 14. In at least one example, the downhole transceiver 100 is coupled with the downhole tool 50. In at least one example, the downhole transceiver 100 is part of the downhole tool 50, such that the downhole tool 50 can be shipped and disposed within the wellbore 14 along with the downhole transceiver 100. In at least one example, the downhole transceiver 100 can be included in a centralizer which maintains the positioning of the downhole tool 50 and/or the conveyance 18 within the wellbore 14. The centralizer may have protrusions which protrude radially from the downhole tool 50 and/or the conveyance and abut against the casing such that the downhole tool 50 and/or the conveyance 18 maintains substantially in the center of the wellbore 14.

FIG. 1B illustrates an exemplary downhole transceiver sub 100. The downhole transceiver sub 100 includes a plurality of electrodes 101 which extend radially from the body of the downhole transceiver sub 100. The downhole transceiver sub 100 can be a part of the downhole tool 50 such that the electrodes 101 extend radially from the body of the downhole tool 50 to be in contact with the casing 14. Additionally or alternately, the downhole transceiver sub 100 can be a part of a centralizer such that the electrodes 101 extend along the protrusions to be in contact with the casing 14. For example, the centralizer may be formed from four bow spring centralizers that centralize the downhole tool 50 and/or the conveyance 18 while being mechanically coupled with the casing 14 via a pad which has a metal plate that can be electrically coupled with the casing 14. The electrodes 101 are operable to transmit an electric current. As such, the electrodes 101 are made of an electrically conductive material, for example aluminum, Brass, Silver, Copper, Gold, Beryllium, magnesium, rhodium, bronze, molybdenum, tungsten, zinc, cobalt, cadmium, nickel, iron, osmium, lithium, tin, selenium, platinum, silicon bronze, tantalum, chromium, steel, zirconium, monel, Inconel, vanadium, Hastelloy, Waspaloy, titanium, graphite, graphene, carbon composites, antimony, alloys thereof, and/or electrodes made of one material (for example Inconel) but coated with another material (for example copper or graphene). The body of the centralizer, downhole tool 50, and/or the conveyance 18 may be at least partially insulated such that contact with the casing 14 does not result in a short circuit. For example, the insulating material can be fiber glass, resin, PEEK, or any suitable material which can withstand the mechanical stresses as well as temperatures and pressures downhole.

The electrodes 101 of the downhole transceiver sub 100 include a first electrode 104 in contact with the casing 14, and a second electrode 102 also in contact with the casing 14. The second electrode 102 is in contact with the casing 14 a distance uphole from the first electrode 104. The distance between the locations that the first and second electrodes 104, 102 are in contact with the casing 14 can be, for example, about 5 feet to about 30 feet. For example, the distance between the first and second electrodes 104, 102 can be any suitable distance such that the downhole tool 50 can be transported without undue burden. In at least one example, the first and second electrodes 104, 102 can be positioned on separate subs. In some examples, one or more subs can be positioned in between the first and second electrodes 104, 102. Accordingly, the size and positioning of the subs can be flexible. In at least one example, the length of the downhole tool 50 can be less than 30 feet.

The electrodes 101 of the downhole transceiver sub 100 are coupled with a current source 112. The current source 112 may be an alternating current source such that current can be passed through the first and second electrodes 104, 102 in an alternating manner. The current source 112 passes a current through the first and second electrodes 104, 102, and the current passes between the first and second electrodes 104, 102 through the electrically conductive casing 14. FIG. 1B illustrates the current passing from the first electrode 104, through the casing 14, and received by the second electrode 102. However, the current can also be passed through the second casing 102, through the casing 14, and received by the first electrode 104. The waveform of the current source 112 can be modulated with an encoded sequence for the telemetry of data. A processing system 109 coupled with the current source 112 and the downhole tool 50 can modulate the waveform accordingly. The processing system 109 is discussed in greater detail in regards to FIG. 4. The data can be provided by, for example, by the downhole tool 50. For example, pressure and/or temperature measurements from sensors of the downhole tool 50 can be transmitted to and received by the processing system 109. The processing system 109 can determine a modulated waveform with an encoded sequence, and control the current source 112 to emit the modulated waveform and pass the modulated waveform between the first and second electrodes 104, 102 through the casing 14.

The highly conductive casing 14 forms a short circuit between the first and second electrodes 104, 102, and the current flowing along the casing 14 forms a finite-length electric dipole antenna which radiates electromagnetic fields into the formation 22.

The electromagnetic fields can be measured uphole from the downhole transceiver sub 100, for example at the surface, using an uphole transceiver sub 190 (see FIG. 1A). The uphole transceiver sub 190 includes a first electrode 192, a second electrode 194 positioned a distance from the first electrode 192, a processing system 199, and a voltmeter 198. The electromagnetic fields are measured by determining the voltage, using the voltmeter 198, between the first electrode 192 and the second electrode 194 of the uphole transceiver sub 190. As illustrated in FIG. 1A, the first electrode 192 is in contact with the casing 14. The first electrode 192 is made of an electrically conductive material such that electric current can be passed through the first electrode 192. The second electrode 194 is coupled with the first electrode 192, and is positioned a distance from the first electrode 192. The second electrode 194, as illustrated in FIG. 1A, is in contact with the ground or the formation 22. The second electrode 194, for example, can be a metal stake, a plurality of metal stakes, a porous pot, an active electrode, or a capacitive electrode. The distance between the first and second electrodes 192, 194 can be, for example, about 50 meters to about 500 meters.

For example, the current source 112 in the downhole transceiver sub 100 may emit a 10 A current (about 1 MW power) between the first and second electrodes 104, 102. The voltage signal measured across first and second electrodes 192, 194 of the uphole transceiver sub 190 which are positioned a distance of about 100 meters apart is about 1.25 mV. The voltage signal of 1.25 mV is significantly higher than the noise level of surface receiver systems used in conventional electromagnetic telemetry systems, which can be in the order of 100 nV. The signal-to-noise levels can be improved by increasing the distance between the first and second electrodes 104, 102 of the downhole transceiver sub 100. In at least one example, there can be feedback from the surface to downhole affecting the quality of the signal, and the downhole transceiver sub 100 can adjust its frequency of transmission to optimize the signal strength. Equalization and signal pre-conditioning can also be utilized if the physical channel layer is determined. Occasional handshaking between the uphole transceiver sub 190 and downhole transceiver sub 100 can establish the physical channel layer.

The processing system 199 is coupled with the voltmeter 198, and receives the voltage reading between the first and second electrodes 192, 194 of the uphole transceiver sub 190. The processing system 199 can decode the measured electromagnetic fields to obtain the data passed from the downhole transceiver sub 100, for example from the downhole tool 50. As the EMT system 60 provides a broad bandwidth, modulation and demodulation of the signals passed by the electromagnetic fields can be performed by a variety of schemes. For example, the scheme for modulation and demodulation can include pulse width modulation (PWM), pulse position modulation (PPM), on-off keying (OOK), amplitude modulation (AM), frequency modulation (FM), single-side-band modulation (SSB), frequency shift keying (FSK), phase shift keying (PSK) such as binary phase shift keying (BPSK), M-ary shift keying (for example, QPSK, 8-QAM), discrete multi-tone (DMT), spread spectrum, and orthogonal frequency division multiplexing (OFDM). In some examples, error correction methods such as forward error correction (for example convolutional codes, frame synchronization, reed-solomon codes, turn codes, and the like) and/or parity checks can be used to correct the data, and/or a downlink signal can be sent from the uphole transceiver sub 190 to the downhole transceiver sub 100, or vice versa, to request the data be resent.

With the EMT system 60 as disclosed herein, a wireless telemetry system for use in case-hold operations is provided. The EMT system 60 can be operated and utilized in oil-based or water-based mud systems. The EMT system 60 can also be operated and utilized in gas wells or any other wells, as the fluid within the wellbore is not necessary to the operation of the EMT system 60.

The EMT system 60 can also be bidirectional in that the uphole transceiver sub 190 can transmit signals to be received by the downhole transceiver sub 100. The operation is similar to the operation described above. The uphole transceiver sub 190 includes a current source 196 coupled with the processing system 199. The processing system 199 may receive a signal, such as instructions for the downhole tool 50, and determines a current with a modulated waveform to be emitted by the current source 196. The current source 196 emits the current with the modulated waveform which passes between the first and second electrodes 192, 194 through the ground, forming a finite-length electric dipole antenna which radiates electromagnetic fields into the formation. The electromagnetic fields can be measured by the downhole transceiver sub 100 by measuring the voltage between the first electrode 104 and the second electrode 102 of the downhole transceiver sub 100 using a voltmeter 110 (as shown in FIG. 1B). The measured electromagnetic fields can then be decoded by the processing system 109 to obtain the data from the uphole transceiver sub 190. For example, if the data from the uphole transceiver sub 190 includes instructions for the downhole tool 50, the processing system 109 may then provide the instructions to the downhole tool 50 to conduct an operation. For example, if the downhole tool 50 includes a valve, the instructions may include opening or closing the valve.

In at least one example, as illustrated in FIG. 1A, the EMT system 60 can also include one or more intermediate subs 150 disposed between the downhole transceiver sub 100 and the uphole transceiver sub 190. In other examples, the EMT system 60 may not include intermediate subs 150. The intermediate subs 150 can function as an azimuthal array of transmitting antennas, such that an electromagnetic signal can be directed purely to a receiver and provide greater depth penetration or data rate capabilities. As such, the intermediate subs 150 can function as signal amplifiers. The intermediate subs 150 can be positioned, for example, at the top of the downhole tool 50 and/or along the conveyance 18.

The intermediate subs 150 can include electrodes 151 similar to the downhole transceiver sub 100. The intermediate subs 150 can include a first electrode 154 in contact with the casing 14 and a second electrode 152 in contact with the casing 14 a distance uphole from the first electrode 154. The distance between the contact points of the first and second electrodes 154, 152 can be, for example, about 5 feet to about 30 feet Similar to the downhole transceiver sub 100, the intermediate subs 150 can be included in centralizers such that the electrodes 151 extend along the protrusions of the centralizers.

FIG. 2 illustrates an example of an EMT system 60 where the uphole transceiver sub 190 includes separate sets of electrodes for transmission and detection. The uphole transceiver sub 190 includes a first electrode 192 and a second electrode 194 as discussed above in regards to FIG. 1A. The first and second electrodes 192, 194 are utilized to transmit signals to the downhole transceiver sub 100 as discussed above. As illustrated in FIG. 2, the uphole transceiver sub 190 can also include a third electrode 293 and a fourth electrode 295. The third and fourth electrodes 293, 295 can both be in contact with the ground or the formation 22. The third and fourth electrodes 293, 295 can be utilized to detect and receive signals from the downhole transceiver sub 100. To do so, the voltage between the third and fourth electrodes 293, 295 are measured by a voltmeter 297 to measure the electromagnetic fields emitted from the downhole transceiver sub 100. The voltmeter 297 is coupled with the processing system 199, and the measured magnetic fields can then be decoded.

FIG. 3 illustrates another example of an EMT system 60 with a modification of the uphole transceiver sub 390. The downhole transceiver sub 100 of the EMT system 60 as illustrated in FIG. 3 is similar to the downhole transceiver sub 100 as discussed above in regards to FIGS. 1A-1B. As illustrated in FIG. 3, a second wellbore 314 is positioned adjacent to the wellbore 14. The second wellbore 314 can include a casing 320. In other examples, the second wellbore 314 is an open hole wellbore. While the second wellbore 314 is illustrated as a vertical wellbore, the second wellbore 314 can have other orientations, including horizontal wellbores, slanted wellbores, multilateral wellbores or the like.

The uphole transceiver 390 can include a first electrode 394 in contact with the ground. For example, as illustrated in FIG. 3, the first electrode 394 can be in contact with the ground at the surface. The uphole transceiver 390 also includes a second electrode 392 which is disposed within the second wellbore 314. For example, the second electrode 392 may be coupled with a conveyance such as coiled tubing or wireline and disposed within the second wellbore 314. As illustrated in FIG. 3, the second electrode 392 is in contact with the casing 320 of the second wellbore 314. As the downhole transceiver sub 100 transmits magnetic fields, the magnetic fields can be measured by measuring the voltage, by a voltmeter 398, between the first and second electrodes 394, 392 of the uphole transceiver sub 390. The voltmeter 398 is coupled with the processing system 399, and the measured magnetic fields can then be decoded.

FIG. 4 is a block diagram of an exemplary processing system 109, 199, 399. Processing system 109, 199, 399 is configured to perform processing of data and communicate with the downhole tools 50, for example as illustrated in FIGS. 1A-3. Additionally, processing system 109, 199, 399 can be utilized with at least one of the downhole transceiver sub 100 and the uphole transceiver sub 190. In operation, processing system 109, 199, 399 communicates with one or more of the above-discussed components and may also be configured to communication with remote devices/systems.

As shown, processing system 109, 199, 399 includes hardware and software components such as network interfaces 410, at least one processor 420, sensors 460 and a memory 440 interconnected by a system bus 450. Network interface(s) 410 can include mechanical, electrical, and signaling circuitry for communicating data over communication links, which may include wired or wireless communication links. Network interfaces 410 are configured to transmit and/or receive data using a variety of different communication protocols, as will be understood by those skilled in the art.

Processor 420 represents a digital signal processor (e.g., a microprocessor, a microcontroller, or a fixed-logic processor, etc.) configured to execute instructions or logic to perform tasks in a wellbore environment. Processor 420 may include a general purpose processor, special-purpose processor (where software instructions are incorporated into the processor), a state machine, application specific integrated circuit (ASIC), a programmable gate array (PGA) including a field PGA, an individual component, a distributed group of processors, and the like. Processor 420 typically operates in conjunction with shared or dedicated hardware, including but not limited to, hardware capable of executing software and hardware. For example, processor 420 may include elements or logic adapted to execute software programs and manipulate data structures 445, which may reside in memory 440.

Sensors 460, which may include sensors of downhole tools 50 as disclosed herein, typically operate in conjunction with processor 420 to perform measurements, and can include special-purpose processors, detectors, transmitters, receivers, and the like. In this fashion, sensors 460 may include hardware/software for generating, transmitting, receiving, detection, logging, and/or sampling magnetic fields, seismic activity, and/or acoustic waves, temperature, pressure, radiation levels, casing collar locations, weights, torques, tool health (such as voltage levels and current monitors), accelerations, gravitational fields, strains, video recordings, flow rates, solids concentration, solids size, chemical composition, and/or other parameters.

Memory 440 comprises a plurality of storage locations that are addressable by processor 420 for storing software programs and data structures 445 associated with the embodiments described herein. An operating system 442, portions of which may be typically resident in memory 440 and executed by processor 420, functionally organizes the device by, inter alia, invoking operations in support of software processes and/or services 444 executing on processing system 109, 199, 399. These software processes and/or services 444 may perform processing of data and communication with processing system 109, 199, 399, as described herein. Note that while process/service 444 is shown in centralized memory 440, some examples provide for these processes/services to be operated in a distributed computing network.

It will be apparent to those skilled in the art that other processor and memory types, including various computer-readable media, may be used to store and execute program instructions pertaining to the fluidic channel evaluation techniques described herein. Also, while the description illustrates various processes, it is expressly contemplated that various processes may be embodied as modules having portions of the process/service 444 encoded thereon. In this fashion, the program modules may be encoded in one or more tangible computer readable storage media for execution, such as with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor, and any processor may be a programmable processor, programmable digital logic such as field programmable gate arrays or an ASIC that comprises fixed digital logic. In general, any process logic may be embodied in processor 420 or computer readable medium encoded with instructions for execution by processor 420 that, when executed by the processor, are operable to cause the processor to perform the functions described herein.

Referring to FIG. 5, a flowchart is presented in accordance with an example embodiment. The method 500 is provided by way of example, as there are a variety of ways to carry out the method. The method 500 described below can be carried out using the configurations illustrated in FIGS. 1A-4, for example, and various elements of these figures are referenced in explaining example method 500. Each block shown in FIG. 5 represents one or more processes, methods or subroutines, carried out in the example method 500. Furthermore, the illustrated order of blocks is illustrative only and the order of the blocks can change according to the present disclosure. Additional blocks may be added or fewer blocks may be utilized, without departing from this disclosure. The example method 500 can begin at block 502.

At block 502, an electric dipole antenna that radiates electromagnetic fields is created. A current is passed between a first electrode and a second electrode of a downhole transceiver sub through a casing in a wellbore. The first electrode is in contact with the casing, and the second electrode is in contact with the casing a distance uphole from the first electrode. Increasing the distance between the contact points of the electrodes can increase the signal-to-noise levels. For example, the distance between the contact points of the first electrode and the second electrode of the downhole transceiver sub can be between about 5 feet and about 30 feet. The downhole transceiver sub can be coupled with a downhole tool which is coupled with a conveyance. The conveyance, with the downhole tool and the downhole transceiver sub, is disposed within the wellbore. Data from the downhole tool can be transmitted to the downhole transceiver sub to be transmitted to an uphole transceiver sub. For example, the downhole tool may include a temperature sensor, and the temperature readings may be transmitted uphole by the downhole transceiver sub.

The downhole transceiver sub includes a processing system which can determine a modulated waveform with an encoded sequence, and control a current source to emit the modulated waveform and pass the modulated waveform between the first and second electrodes through the casing. The current can be an alternating current. The electrically conductive casing forms a short circuit between the first and second electrodes of the downhole transceiver sub, and the current forms a finite-length electric dipole antenna which radiates electromagnetic fields into the formation.

In at least one example, the magnetic fields can be amplified using one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and the uphole transceiver sub. The intermediate subs can each include a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode.

At block 504, the magnetic fields are measured by measuring a voltage between a first electrode and a second electrode of an uphole transceiver sub which is positioned uphole form the downhole transceiver sub. In at least one example, the first electrode of the uphole transceiver sub is in contact with the casing, and the second electrode of the uphole transceiver sub is in contact with the ground a distance from the first electrode.

At block 506, the data is determined by a processor by decoding the measured magnetic fields. The processing system, including the processor, can decode the measured electromagnetic fields to obtain the data passed from the downhole transceiver sub, for example from the downhole tool. In at least one example, there can be feedback from the surface to downhole affecting the quality of the signal, and the downhole transceiver sub 100 can adjust its frequency of transmission to optimize the signal strength. Equalization and signal pre-conditioning can also be utilized if the physical channel layer is determined. Occasional handshaking between the uphole transceiver sub 190 and downhole transceiver sub 100 can establish the physical channel layer.

As the EMT system provides a broad bandwidth, modulation and demodulation of the signals passed by the electromagnetic fields can be performed by a variety of schemes. For example, the scheme for modulation and demodulation can include pulse width modulation (PWM), pulse position modulation (PPM), on-off keying (OOK), amplitude modulation (AM), frequency modulation (FM), single-side-band modulation (SSB), frequency shift keying (FSK), phase shift keying (PSK) such as binary phase shift keying (BPSK), M-ary shift keying (for example, QPSK, 8-QAM), discrete multi-tone (DMT), spread spectrum, and orthogonal frequency division multiplexing (OFDM). In some examples, error correction methods such as forward error correction (for example convolutional codes, frame synchronization, reed-solomon codes, turn codes, and the like) and/or parity checks can be used to correct the data, and/or a downlink signal can be sent from the uphole transceiver sub to the downhole transceiver sub, or vice versa, to request the data be resent.

As the EMT system is bidirectional, the uphole transceiver sub can transmit signals to be received by the downhole transceiver sub. Current is passed between the first and second electrodes of the uphole transceiver sub which forms an electric dipole antenna. The voltage between the first and second electrodes of the downhole transceiver sub can be measured to measure the electromagnetic fields from the electric dipole antenna. The measured electromagnetic fields can then be decoded to obtain the data from uphole, or from the tool connected to the uphole transceiver sub. In at least one example, based on the data from uphole, for example the surface, the downhole tool may be adjusted. For example, if the downhole tool includes a valve, the signal may instruct the downhole tool to open or close the valve. Accordingly, the EMT system disclosed herein provides for a wireless telemetry system within a cased wellbore.

Numerous examples are provided herein to enhance understanding of the present disclosure. A specific set of statements are provided as follows.

Statement 1: An electromagnetic telemetry (EMT) system is disclosed comprising: a downhole transceiver sub operable to be coupled with a downhole tool, the downhole transceiver sub and the downhole tool operable to be positioned in a wellbore having a casing extending along a length of the wellbore, the downhole transceiver sub operable to transmit data from the downhole tool by passing a current through the casing to radiate electromagnetic fields; and an uphole transceiver sub operable to be disposed uphole from the downhole transceiver sub, the uphole transceiver sub is operable to measure the electromagnetic fields, wherein the measured electromagnetic fields are decoded to obtain the data from the downhole tool.

Statement 2: An EMT system is disclosed according to Statement 1, wherein the downhole transceiver sub further comprises: a first electrode operable to be in contact with the casing, and a second electrode operable to be in contact with the casing a distance uphole from the first electrode, wherein the current is passed between the first electrode and the second electrode through the casing to form an electric dipole antenna which radiates the electromagnetic fields.

Statement 3: An EMT system is disclosed according to Statement 2, wherein the downhole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the downhole transceiver sub.

Statement 4: An EMT system is disclosed according to Statements 2 or 3, wherein the distance between the first electrode and the second electrode of the downhole transceiver sub is between about 5 feet and about 30 feet.

Statement 5: An EMT system is disclosed according to any of preceding Statements 1-4, wherein the uphole transceiver sub further comprises: a first electrode, and a second electrode, the second electrode being disposed a distance from the first electrode, wherein the electromagnetic fields are measured by the voltage between the first electrode and the second electrode of the uphole transceiver sub.

Statement 6: An EMT system is disclosed according to Statement 5, wherein the first electrode of the uphole transceiver sub is operable to be in contact with the casing, and the second electrode of the uphole transceiver sub is operable to be in contact with the ground.

Statement 7: An EMT system is disclosed according to Statements 5 or 6, wherein the uphole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the uphole transceiver sub.

Statement 8: An EMT system is disclosed according to any of preceding Statements 1-7, further comprising one or more intermediate subs operable to be disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode operable to be in contact with the casing and a second electrode operable to be in contact with the casing a distance uphole from the first electrode, wherein the one or more intermediate subs are operable to be function as signal amplifiers.

Statement 9: An EMT system is disclosed according to any of preceding Statements 1-8, further comprising a processor coupled with the uphole transceiver sub, the processor configured to determine the data by demodulating the measured magnetic fields.

Statement 10: A system is disclosed comprising: a conveyance disposed within a wellbore having a casing extending along a length of the wellbore; a downhole tool coupled with the conveyance; an electromagnetic telemetry (EMT) system coupled with the downhole tool, the EMT system operable to transmit information from the downhole tool, the EMT system comprising: a downhole transceiver sub coupled with a downhole tool, the downhole transceiver sub and the downhole tool positioned in a wellbore having a casing extending along a length of the wellbore, the downhole transceiver sub transmitting data from the downhole tool by passing a current through the casing to radiate electromagnetic fields; and an uphole transceiver sub disposed uphole from the downhole transceiver sub, the uphole transceiver sub is operable to measure the electromagnetic fields, wherein the measured electromagnetic fields are decoded to obtain the data from the downhole tool.

Statement 11: A system is disclosed according to Statement 10, wherein the downhole transceiver sub further comprises: a first electrode in contact with the casing, and a second electrode in contact with the casing a distance uphole from the first electrode, wherein the current is passed between the first electrode and the second electrode through the casing to form an electric dipole antenna which radiates the electromagnetic fields.

Statement 12: A system is disclosed according to Statements 10 or 11, wherein the uphole transceiver sub further comprises: a first electrode, and a second electrode, the second electrode being disposed a distance from the first electrode, wherein the electromagnetic fields are measured by the voltage between the first electrode and the second electrode of the uphole transceiver sub.

Statement 13: A system is disclosed according to Statement 12, wherein the first electrode of the uphole transceiver sub is in contact with the casing, and the second electrode of the uphole transceiver sub is in contact with the ground.

Statement 14: A system is disclosed according to Statements 12 or 13, wherein the uphole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the uphole transceiver sub.

Statement 15: A system is disclosed according to any of preceding Statements 10-14, further comprising one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and uphole transceiver sub, the one or more intermediate subs each including a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode, wherein the one or more intermediate subs function as signal amplifiers.

Statement 16: A system is disclosed according to any of preceding Statements 10-15, further comprising a processor coupled with the uphole transceiver sub, the processor configured to determine the data by demodulating the measured magnetic fields.

Statement 17: A method is disclosed to use an electromagnetic telemetry (EMT) system, the method comprising: creating an electric dipole antenna which radiates electromagnetic fields to transmit data using a downhole transceiver sub disposed in a wellbore; measuring the magnetic fields by an uphole transceiver sub which is positioned uphole from the downhole transceiver sub; and determining, by a processor, the data by decoding the measured magnetic fields.

Statement 18: A method is disclosed according to Statement 17, wherein creating an electric dipole antenna includes passing a current between a first electrode of a downhole transceiver sub and a second electrode of the downhole transceiver sub through the casing, the first electrode in contact with the casing, and the second electrode of the downhole transceiver sub in contact with the casing a distance uphole from the first electrode, wherein measuring the magnetic fields includes measuring a voltage between a first electrode and a second electrode of the uphole transceiver sub.

Statement 19: A method is disclosed according to Statements 17 or 18, further comprising: disposing a conveyance in the wellbore, a downhole tool being coupled with the conveyance, the downhole transceiver sub being coupled with the downhole tool; transmitting the data from the downhole tool to the downhole transceiver sub.

Statement 20: A method is disclosed according any of Statements 17-19, further comprising: amplifying the magnetic fields using one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode.

The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, especially in matters of shape, size and arrangement of the parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms used in the attached claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the appended claims. 

What is claimed is:
 1. An electromagnetic telemetry (EMT) system comprising: a downhole transceiver sub operable to be coupled with a downhole tool, the downhole transceiver sub and the downhole tool operable to be positioned in a wellbore having a casing extending along a length of the wellbore, the downhole transceiver sub operable to transmit data from the downhole tool by passing a current through the casing to radiate electromagnetic fields; and an uphole transceiver sub operable to be disposed uphole from the downhole transceiver sub, the uphole transceiver sub is operable to measure the electromagnetic fields, wherein the measured electromagnetic fields are decoded to obtain the data from the downhole tool.
 2. The EMT system of claim 1, wherein the downhole transceiver sub further comprises: a first electrode operable to be in contact with the casing, and a second electrode operable to be in contact with the casing a distance uphole from the first electrode, wherein the current is passed between the first electrode and the second electrode through the casing to form an electric dipole which radiates the electromagnetic fields.
 3. The EMT system of claim 2, wherein the downhole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the downhole transceiver sub.
 4. The EMT system of claim 2, wherein the distance between the first electrode and the second electrode of the downhole receiver sub is between about 5 feet and about 30 feet.
 5. The EMT system of claim 1, wherein the uphole transceiver sub further comprises: a first electrode, and a second electrode, the second electrode being disposed a distance from the first electrode, wherein the electromagnetic fields are measured by the voltage between the first electrode and the second electrode of the uphole transceiver sub.
 6. The EMT system of claim 5, wherein the first electrode of the uphole transceiver sub is operable to be in contact with the casing, and the second electrode of the uphole transceiver sub is operable to be in contact with the ground.
 7. The EMT system of claim 5, wherein the uphole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the uphole transceiver sub.
 8. The EMT system of claim 1, further comprising one or more intermediate subs operable to be disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode operable to be in contact with the casing and a second electrode operable to be in contact with the casing a distance uphole from the first electrode, wherein the one or more intermediate subs are operable to be function as signal amplifiers.
 9. The EMT system of claim 1, further comprising a processor coupled with the uphole transceiver sub, the processor configured to determine the data by demodulating the measured magnetic fields.
 10. A system comprising: a conveyance disposed within a wellbore having a casing extending along a length of the wellbore; a downhole tool coupled with the conveyance; an electromagnetic telemetry (EMT) system coupled with the downhole tool, the EMT system operable to transmit information from the downhole tool, the EMT system comprising: a downhole transceiver sub coupled with a downhole tool, the downhole transceiver sub and the downhole tool positioned in a wellbore having a casing extending along a length of the wellbore, the downhole transceiver sub transmitting data from the downhole tool by passing a current through the casing to radiate electromagnetic fields; and an uphole transceiver sub disposed uphole from the downhole transceiver sub, the uphole transceiver sub is operable to measure the electromagnetic fields, wherein the measured electromagnetic fields are decoded to obtain the data from the downhole tool.
 11. The system of claim 10, wherein the downhole transceiver sub further comprises: a first electrode in contact with the casing, and a second electrode in contact with the casing a distance uphole from the first electrode, wherein the current is passed between the first electrode and the second electrode through the casing to form an electric dipole which radiates the electromagnetic fields.
 12. The system of claim 10, wherein the uphole transceiver sub further comprises: a first electrode, and a second electrode, the second electrode being disposed a distance from the first electrode, wherein the electromagnetic fields are measured by the voltage between the first electrode and the second electrode of the uphole transceiver sub.
 13. The system of claim 12, wherein the first electrode of the uphole transceiver sub is in contact with the casing, and the second electrode of the uphole transceiver sub is in contact with the ground.
 14. The system of claim 12, wherein the uphole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the uphole transceiver sub.
 15. The system of claim 10, further comprising one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode, wherein the one or more intermediate subs function as signal amplifiers.
 16. The system of claim 10, further comprising a processor coupled with the uphole transceiver sub, the processor configured to determine the data by demodulating the measured magnetic fields.
 17. A method to use an electromagnetic telemetry (EMT) system, the method comprising: creating an electric dipole which radiates electromagnetic fields to transmit data using a downhole transceiver sub disposed in a wellbore; measuring the magnetic fields by an uphole transceiver sub which is positioned uphole from the downhole transceiver sub; and determining, by a processor, the data by decoding the measured magnetic fields.
 18. The method of claim 17, wherein creating an electric dipole includes passing a current between a first electrode of a downhole transceiver sub and a second electrode of the downhole transceiver sub through the casing, the first electrode in contact with the casing, and the second electrode of the downhole transceiver sub in contact with the casing a distance uphole from the first electrode, wherein measuring the magnetic fields includes measuring a voltage between a first electrode and a second electrode of the uphole transceiver sub.
 19. The method of claim 17, further comprising: disposing a conveyance in the wellbore, a downhole tool being coupled with the conveyance, the downhole transceiver sub being coupled with the downhole tool; transmitting the data from the downhole tool to the downhole transceiver sub.
 20. The method of claim 17, further comprising: amplifying the magnetic fields using one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode. 